Nuclear targeting of DNA

Ultrasound‑targeted microbubbles combined with a peptide nucleic acid binding nuclear localization signal mediate transfection of exogenous genes by improving cytoplasmic and nuclear import

The development of an efficient delivery system is critical for the successful treatment of cardiovascular diseases using non-viral gene therapies. Cytoplasmic and nuclear membrane barriers reduce delivery efficiency by impeding the transfection of foreign genes. Thus, a gene delivery system capable of transporting exogenous genes may improve gene therapy. The present study used a novel strategy involving ultrasound-targeted microbubbles and peptide nucleic acid (PNA)-binding nuclear localization signals (NLS). Ultrasound-targeted microbubble destruction (UTMD) and PNA-binding NLS were used to improve the cytoplasmic and nuclear importation of the plasmid, respectively. Experiments were performed using antibody-targeted microbubbles (AT-MCB) that specifically recognize the SV40T antigen receptor expressed on the membranes of 293T cells, resulting in the localization of ultrasound microbubbles to 293T cell membranes. Furthermore, PNA containing NLS was inserted into the enhanced green fluorescent protein (EGFP)-N3 plasmid DNA (NLS-PNA-DNA), which increased nuclear localization. The nuclear import and gene expression efficiency of the AT-MCB with PNA-binding NLS were compared with AT-MCB alone or a PNA-binding NLS. The effect of the AT-MCB containing PNA-binding NLS on transfection was investigated. The ultrasound and AT-MCB delivery significantly enhanced the cytoplasmic intake of exogenous genes and maintained high cell viability. The nuclear import and gene expression of combined microbubble- and PNA-transfected cells were significantly greater compared with cells that were transfected with AT-MCB or DNA with only PNA-binding NLS. The quantity of EGFP-N3 plasmids in the nuclei was increased by >5.0-fold compared with control microbubbles (CMCB) and NLS-free plasmids. The gene expression was ~1.7-fold greater compared with NLS-free plasmids and 1.3-fold greater compared with control microbubbles. In conclusion, UTMD combined with AT-MCB and a PNA-binding NLS plasmid significantly improved transfection efficiency by increasing cytoplasmic and nuclear DNA import. This method is a promising strategy for the noninvasive and effective delivery of target genes or drugs for the treatment of cardiovascular diseases.

Bacteriophage receptor recognition and nucleic acid transfer

Correct host cell recognition is important in the replication cycle for any virus, including bacterial viruses. This essential step should occur before the bacteriophage commits to transfer its genomic material into the host. In this chapter we will discuss the proteins and mechanisms bacteriophages use for receptor recognition (just before full commitment to infection) and nucleic acid injection, which occurs just after commitment. Some bacteriophages use proteins of the capsid proper for host cell recognition, others use specialised spikes or fibres. Usually, several identical recognition events take place, and the information that a suitable host cell has been encountered is somehow transferred to the part of the bacteriophage capsid involved in nucleic acid transfer. The main part of the capsids of bacteriophages stay on the cell surface after transferring their genome, although a few specialised proteins move with the DNA, either forming a conduit, protecting the nucleic acids after transfer and/or functioning in the process of transcription and translation.

The use of size-defined DNA-functionalized calcium phosphate nanoparticles to minimise intracellular calcium disturbance during transfection

Calcium phosphate-based transfection methods are frequently used to transfer DNA into living cells. However, it has so far not been studied in detail to what extend the different transfection methods lead to a net calcium uptake. Upon subsequent resolution of the calcium phosphate, intracellular free ionic calcium-surges could result, inducing as side effect various physiological responses that may finally result in cell death. Here we investigated the overall calcium uptake by the human bladder carcinoma cell line T24 during the standard calcium phosphate transfection method and also during transfection with custom-made calcium phosphate/DNA nanoparticles by isotope labelling with (45)calcium. (45)Calcium uptake was strongly increased after 7h of standard calcium phosphate transfection but not if the transfection was performed with calcium phosphate nanoparticles. Time lapse imaging microscopy using the calcium-sensitive dye Fura-2 revealed large transient increases of the intracellular free calcium level during the standard calcium phosphate transfection but not if calcium phosphate nanoparticles were used. Consistently, the viability of cells transfected by calcium phosphate/DNA nanoparticles was not changed, in remarkable contrast to the standard method where considerable cell death occurred.

Nanoparticles as nonviral gene delivery vectors

Gene therapy, as therapeutic treatment to genetic or acquired diseases, is attracting much interest in the research community, leading to noteworthy developments over the past two decades. Although this field is still dominated by viral vectors, nonviral vectors have recently received an ever increasing attention in order to overcome the safety problems of their viral counterpart. This review presents the biological aspects involved in the gene delivery process and explores the recent developments and achievements of nonviral gene carriers.

Vault ribonucleoprotein particles and the central mass of the nuclear pore complex

Nuclear pore complexes (NPCs) are macromolecular pores that span the nuclear envelope and undergo conformational changes in response to changes in cisternal calcium levels. Depletion of cisternal calcium leads to the appearance of a mass within the pore. The identity and role of this central mass remain unknown, although some studies suggest they are vault complexes. Vault complexes are 13 MDa ribonucleoproteins found in the cytoplasm and recently in the nuclei of some species, suggesting that they associate with NPCs to cross the nuclear envelope. Using Förster resonance energy transfer (FRET) measurements between labeled vaults and NPCs, we find significant energy transfer suggesting that vaults and NPCs are closely associated at the nuclear envelope. This is supported by high-resolution electron microscopy measurements revealing significant spatial correlations between gold-labeled vaults and NPCs. As the location of the central mass in the NPC is dependent on cisternal calcium levels, FRET signals under conditions of varying cisternal calcium were also measured and shown to undergo significant changes. Together, these findings suggest that the central mass observed in NPCs may be, at least in part, due to the presence of vaults in the pore. Possible roles in cyto-nuclear trafficking are discussed.

Biodegradable nanoparticles for cytosolic delivery of therapeutics

Many therapeutics require efficient cytosolic delivery either because the receptors for those drugs are located in the cytosol or their site of action is an intracellular organelle that requires transport through the cytosolic compartment. To achieve efficient cytosolic delivery of therapeutics, different nanomaterials have been developed that consider the diverse physicochemical nature of therapeutics (macromolecule to small molecule; water soluble to water insoluble) and various membrane associated and intracellular barriers that these systems need to overcome to efficiently deliver and retain therapeutics in the cytoplasmic compartment. Our interest is in investigating PLGA and PLA-based nanoparticles for intracellular delivery of drugs and genes. The present review discusses the various aspects of our studies and emphasizes the need for understanding of the molecular mechanisms of intracellular trafficking of nanoparticles in order to develop an efficient cytosolic delivery system.

Nuclear localisation and pDNA condensation in non-viral gene delivery

BACKGROUND

Non-viral gene delivery vectors are multi-component systems reflecting various functionalities required for effective cell transfection, including DNA condensation, promotion of cell membrane interactions and provision for subcellular targeting through endosomal escape and/or nuclear delivery. Elements mediating these functions will clearly display inter-dependency. In this study we sought to explore the relationship within non-viral vectors of condensation and nuclear localisation.

METHODS

Binary, tertiary and quaternary vectors were prepared with combinations of pDNA, DOTAP lipid, the polycation peptide protamine and either SV40 nuclear localisation sequence peptide ('SV40 NLS') or a one amino acid substituted mutant of SV40 NLS ('mutant sequence'). The efficiency of pDNA condensation was determined by gel electrophoresis and quantitative fluorescence spectroscopy. Transfection efficiency was examined in mammalian cells in vitro using standard methods, by electroporation to bypass the plasma membrane barrier and in cells arrested in G0/G1 cell cycle phase to examine the effect of cell division and nuclear membrane disruption.

RESULTS

Small NLS peptide sequences, despite possessing a significant proportion of basic amino acids, display minimal pDNA-condensing ability when compared to larger polycations such as protamine. In standard in vitro cell adherent transfection studies the predominant elements affording enhanced gene expression were effective pDNA condensation and lipid enhancement of cell membrane interactions. These features conversely hinder efficient gene expression in cells that have undergone electroporation. The benefit of SV40 NLS was only apparent when used in non-dividing cell populations.

CONCLUSIONS

Whilst effective levels of non-viral-mediated gene expression generally rely on efficient condensation of pDNA and enhanced interactions with cellular membranes, non-covalently associated NLS within a multi-component non-viral gene vector appears to contribute benefit in sustaining gene expression in non-dividing cells.

Polyethylenimine-based non-viral gene delivery systems

Gene therapy has become a promising strategy for the treatment of many inheritable or acquired diseases that are currently considered incurable. Non-viral vectors have attracted great interest, as they are simple to prepare, rather stable, easy to modify and relatively safe, compared to viral vectors. Unfortunately, they also suffer from a lower transfection efficiency, requiring additional effort for their optimization. The cationic polymer polyethylenimine (PEI) has been widely used for non-viral transfection in vitro and in vivo and has an advantage over other polycations in that it combines strong DNA compaction capacity with an intrinsic endosomolytic activity. Here, we give some insight into strategies developed for PEI-based non-viral vectors to overcome intracellular obstacles, including the improvement of methods for polyplex preparation and the incorporation of endosomolytic agents or nuclear localization signals. In recent years, PEI-based non-viral vectors have been locally or systemically delivered, mostly to target gene delivery to tumor tissue, the lung or liver. This requires strategies to efficiently shield transfection polyplexes against non-specific interaction with blood components, extracellular matrix and untargeted cells and the attachment of targeting moieties, which allow for the directed gene delivery to the desired cell or tissue. In this context, materials, facilitating the design of novel PEI-based non-viral vectors are described.

Optimization of nuclear localization signal for nuclear transport of DNA-encapsulating particles

The nuclear membrane is a tight barrier against the delivery of therapeutic genes into non-dividing tissue cells. Overcoming this barrier with the aid of peptidic nuclear localization signals (NLS) is crucial for improving the performance of synthetic gene-delivery vehicles. In this article, we examine the nuclear transport of lambda phage particles displaying various peptides containing the minimum NLS of SV40 T antigen on their surface. As the minimum NLS (PKKKRKV) is a binding domain to importin alpha, recombinant proteins and molecular conjugates containing this peptide accumulate into the nucleus efficiently. However, we find that the C-terminal and N-terminal structures besides the minimum NLS profoundly affect the efficiency of the nuclear transport of the phage particles as well as their binding capacity to importin alpha: either truncation of a few amino acid residues from the C-terminus or the replacement of the N-terminus with a FLAG- or c-myc-tag abolish both of these biological activities. The structure of the optimized NLS is unpredictable from conventional protein transport assay and from the structural analysis in silico. Our results reveal that the objects with 50 nm in diameter can pass through the nuclear pore complex when the optimized NLS is displayed at a sufficient density on their surface.

Bioconjugated Nanoparticle for DNA Protection from Ultrasound Damage

To research whether poly-L-lysine-starch nanoparticle (PLL-StNP) could protect DNA from ultrasound damage or not, a series experiments were carried out: plasmid DNA-PLL-StNP complexes were treated with ultrasound for diverse times; the electrophoresis result proved that DNA bound to the complexes all the same. To investigate whether the conjugated DNA was completely protected or not, cDNA fragments bound to PLL-StNP were treated with ultrasound, and matched molecular beacons (MBs) were added. The cDNA-MB-PLL-StNP complexes exhibited dramatically increasing fluorescence, and had the same intensity as that of those MBs that were hybridized with free cDNA fragments. After being treated by ultrasound, the pIRGFP plasmid DNA-PLL-StNP complexes were transferred into COS-7 cells mediated by ultrasound. Green fluorescence protein expressed in most of the cells. Those results indicated that PLL-StNP could completely protect DNA from ultrasound damage. Furthermore, the DNA kept the same function as untreated one.

A model for the analysis of nonviral gene therapy

Further understanding of the mechanisms involved in cellular and intracellular delivery of transgene is needed to produce clinical applications of gene therapy. The compartmental and computational model designed in this work is integrated with data from previous experiments to quantitatively estimate rate constants of plasmid translocation across cellular barriers in transgene delivery in vitro. The experimental conditions between two cellular studies were held constant, varying only the cell type, to investigate how the rates differed between cell lines. Two rate constants were estimated per barrier for active transport and passive diffusion. Translocation rates of intact plasmid across the cytoplasmic and nuclear barriers varied between cell lines. CV1 cells were defined by slower rates (0.23 h(-1) cytoplasmic, 0.08 h(-1) nuclear) than those of the HeLa cells (1.87 h(-1) cytoplasmic, 0.45 h(-1) nuclear). The nuclear envelope was identified as a rate-limiting barrier by comparing the rate of intact plasmid translocation at each barrier. Slower intact plasmid translocation in CV1 cells was correlated with a reduced absolute capacity for transgene efficiency in comparison with HeLa cells. HeLa cells were three times more efficient than CV1 cells at producing green fluorescent protein per intact plasmid delivered to the nucleus. Mathematical modeling coordinated with experimental studies can provide detailed, quantitative understanding of nonviral gene therapy.

Nanoparticles of compacted DNA transfect postmitotic cells

Charge-neutral DNA nanoparticles have been developed in which single molecules of DNA are compacted to their minimal possible size. We speculated that the small size of these DNA nanoparticles may facilitate gene transfer in postmitotic cells, permitting nuclear uptake across the 25-nm nuclear membrane pore. To determine whether DNA nanoparticles can transfect nondividing cells, growth-arrested neuroblastoma and hepatoma cells were transfected with DNA/liposome mixtures encoding luciferase. In both models, growth-arrested cells were robustly transfected by compacted DNA (6,900-360-fold more than naked DNA). To evaluate mechanisms responsible for enhanced transfection, HuH-7 cells were microinjected with naked or compacted plasmids encoding enhanced green fluorescent protein. Cytoplasmic microinjection of DNA nanoparticles generated a approximately 10-fold improvement in transgene expression as compared with naked DNA; this enhancement was reversed by the nuclear pore inhibitor, wheat germ agglutinin. To determine the upper size limit for gene transfer, DNA nanoparticles of various sizes were microinjected into the cytoplasm. A marked decrease in transgene expression was observed as the minor ellipsoidal diameter approached 25 nm. In summary, suitably sized DNA nanoparticles productively transfect growth arrested cells by traversing the nuclear membrane pore.

Enhancement of phage-mediated gene transfer by nuclear localization signal

The cell membrane and the nuclear membrane are two major barriers hindering the free movement of various macromolecules through animal cells. Nevertheless, some proteins can actively bypass these barriers by dint of intrinsic peptidic signals, so incorporation of these signals might improve the efficacy of artificial gene delivery vehicles. We examined the role of the nuclear localization signal (NLS) in gene transfer, using recombinant lambda phage as a model of the polymer/DNA complexes. We prepared a lambda phage displaying a 32-mer NLS of SV40 T antigen on its surface (NLS phage), and found that this NLS phage, delivered into the cytoplasm by appropriate devices, has higher affinity for the nucleus and induces the expression of encapsulated marker genes more efficiently than does the wild-type phage. This suggests that the 32-mer NLS peptide will become a practical tool for artificial gene delivery vehicles with enhanced nuclear targeting activity.

Improved neurotensin-vector-mediated gene transfer by the coupling of hemagglutinin HA2 fusogenic peptide and Vp1 SV40 nuclear localization signal

Recently we reported that neurotensin-SPDP-poly-L-lysine (NT-vector) is able to bind plasmid DNA (NT-polyplex) and polyfect cells expressing the high-affinity neurotensin receptor (NTRH) although with low transfecting efficiency: in vitro, 6.5+/-1.5%, and in vivo, 5+/-4%. In this work, we attempted to increase the transfecting efficiency by integrating the hemagglutinin HA2 fusogenic peptide and the Vp1 nuclear localization signal of SV40 to the NT-polyplex (fusogenic-karyophilic-NT-polyplex). Confocal microscopy and flow cytometry analysis showed that the fusogenic-karyophilic-NT-polyplex produced mostly nuclear localization of the plasmid DNA in NTRH-bearing N1E-115 cells. About 50% of N1E-115 cells internalized and expressed the reporter gene when the plasmid DNA was transferred by the fusogenic-karyophilic-NT-polyplex. Although to a less extent, the addition of each viral peptide separately to NT-polyplex (fusogenic-NT-polyplex or karyophilic-NT-polyplex) improved polyfection. Fusogenic-NT-polyplex produced 22.41+/-5.96% of internalization and 20.35+/-0.82% of expression in N1E-115 cells, whereas karyophilic-NT-polyplex yielded 13.75+/-3.88% and 10.94+/-2.04%, respectively. Basal internalization and expression were detected in N1E-115 cells in the presence of 100 nM SR-48692 and in NTRH-lacking cells. The fusogenic-karyophilic-NT-polyplex was microinjected into the substantia nigra to test its ability for gene transfer in vivo. Fusogenic-karyophilic-NT-polyplex internalization was observed within dopamine neurons only. Reporter gene expression was observed in a high proportion of dopamine neurons up to 60 days after NT-polyfection. Both internalization and expression were prevented by SR-48692. Our results show that the fusogenic-karyophilic-NT-polyplex is a highly efficient and specific gene vector and encourage its use to transfer gene of physiological interest to NTRH-bearing neurons.

Regulation of nuclear pore complex conformation by IP(3) receptor activation

In recent years, both the molecular architecture and functional dynamics of nuclear pore complexes (NPCs) have been revealed with increasing detail. These large, supramolecular assemblages of proteins form channels that span the nuclear envelope of cells, acting as crucial regulators of nuclear import and export. From the cytoplasmic face of the nuclear envelope, nuclear pore complexes exhibit an eightfold symmetric ring structure encompassing a central lumen. The lumen often appears occupied by an additional structure alternatively referred to as the central granule, nuclear transport complex, or nuclear plug. Previous studies have suggested that the central granule may play a role in mediating calcium-dependent regulation of diffusion across the nuclear envelope for intermediate sized molecules (10-40 kDa). Using atomic force microscopy to measure the surface topography of chemically fixed Xenopus laevis oocyte nuclear envelopes, we present measurements of the relative position of the central granule within the NPC lumen under a variety of conditions known to modify nuclear Ca(2+) stores. These measurements reveal a large, approximately 9-nm displacement of the central granule toward the cytoplasmic face of the nuclear envelope under calcium depleting conditions. Additionally, activation of nuclear inositol triphosphate (IP(3)) receptors by the specific agonist, adenophostin A, results in a concentration-dependent displacement of central granule position with an EC(50) of ~1.2 nM. The displacement of the central granule within the NPC is observed on both the cytoplasmic and nucleoplasmic faces of the nuclear envelope. The displacement is blocked upon treatment with xestospongin C, a specific inhibitor of IP(3) receptor activation. These results extend previous models of NPC conformational dynamics linking central granule position to depletion of IP(3) sensitive nuclear envelope calcium stores.